DPI-related APIs and registry settings

In this article

If you need to perform deployment customizations, the following sections explain the registry keys and system parameters that your post-installation scripts might need to access.

In this topic:

Primary display native resolution

Primary display DPI scale factor

Scaling mode

Scaling override in Windows 8.1 scaling mode

System-wide scale factor in Windows 8 scaling mode

Simplest mitigation for 125% displays

Mitigation for 150% displays

Primary display native resolution

Table 1 Windows 8.1 Scaling Levels, while by no means exhaustive, provides information on the Windows 8.1 scaling level for a number of common displays. Panel DPI indicates the physical pixel density of the panel, and Scaling level indicates the scale factor that will be used for this display.

Table 1 Windows 8.1 Scaling Levels

Display size

Display resolution

Horizontal (pixels)

Vertical (pixels)

Panel DPI

Scaling level

10.6"

FHD

1920

1080

208

150%

10.6"

HD

1366

768

148

100%

11.6"

WUXGA

1920

1200

195

150%

11.6"

HD

1366

768

135

100%

13.3"

WUXGA

1920

1200

170

150%

13.3"

QHD

2560

1440

221

200%

13.3"

HD

1366

768

118

100%

15.4"

FHD

1920

1080

143

125%

15.6"

QHD+

3200

1800

235

200%

17"

FHD

1920

1080

130

125%

23”

QFHD (4K)

3840

2160

192

200%

24"

QHD

2560

1440

122

125%

To programmatically find this information for any device, you can write a utility program that reports back data. The native primary resolution is retrieved by calling the API GetDeviceCaps() function, using the hdc for the desktop and the HORZRES and VERZRES indices:

Scaling mode

The Control Panel\ Appearance and Personalization\Display user interface (UI) includes a checkbox: Let me choose one scaling level for all my displays, which controls whether the system applies a single scale factor to all displays (as in Windows® 8 and earlier versions of Windows), or different scale factors that take into account the pixel density of each display (the Windows 8.1 default). This checkbox configures the HKCU\Control Panel\Desktop\Win8DpiScaling registry key in Windows 8.1.

Table 3 HKCU\Control Panel\Desktop\Win8DpiScaling Values

Key value

Meaning

0

Different scale factors for each display: Windows 8.1 default.Content that is moved from one display to another will be the right size, but can be bitmap-scaled.

1

Same scale factor is applied to all displays: Windows 8 and earlier Windows versions behavior.Content that is moved from one display to another might be the wrong size

Scaling override in Windows 8.1 scaling mode

When the Let me choose one scaling level for all my displays checkbox is cleared and the system is running in the Windows 8.1 scaling mode, the user is provided with a slider that lets them override the current scale factors, from Smaller, to Medium, to Larger. This setting is configured in the HKCU\Control Panel\Desktop\DesktopDPIOverride registry key.

Table 4 HKCU\Control Panel\Desktop\DesktopDPIOverride Values

Key value

Meaning

<0

Reduce each display scale factor from the default by this value (for example, if the default was 150% scaling, -1 corresponds to 125%, -2 to 100%).

0

Use the default value for each display.

0>

Increase each display factor by this value (using the previous example, +1 corresponds to 200% scaling).

All display scale factors in this mode are constrained to be one of these four values: 100%, 125%, 150%, 200%. In addition, after scaling is applied, applications expect to have at least 720 effective lines of resolution (that is, the physical vertical resolution of the display divided by the scale factor); this can further limit the range of allowed display scale factors. Table 5 Display Values shows which values are allowed for different sized displays:

Table 5 Display Values

Vertical lines

Supported scale factors

<900

100%

>= 900 and <1080

100%, 125%

>=1080 and <1440

100%, 125%, 150%

>=1440

100%, 125%, 150%, 200%

System-wide scale factor in Windows 8 scaling mode

When the Let me choose one scaling level for all my displays checkbox is checked, the user can specify a scale factor that applies to all displays, regardless of each display’s pixel density. By using the custom setting, the user can select values other than 100%, 125%, 150%, 200%, although they are limited to the range (100%-500%). This setting is configured in the HKCU\ControlPanel\Desktop\LogPixels registry key.

Table 6 HKCU\ControlPanel\Desktop\LogPixels Values

Key value

Meaning

96

100% scaling on every display

120

125% scaling on every display

144

150% scaling on every display

192

200% scaling on every display

<other>

<other>*100/96 scaling on every display

Simplest mitigation for 125% displays

The simplest generic fix is to place the system in single-scale-factor mode with a scale factor of 125%. This is not recommended unless the enterprise environment includes a large number of apps that aren’t DPI-aware and that scale poorly at 125%. In pseudo-code this would look something like this:

If (verticalResolution < 1080) and (DPI == 125%)
Set HKCU\...\Win8DPIScaling to 1
Set HKCU\...\LogPixels to 120
Require logoff/logon

Mitigation for 150% displays

For more pixel-dense displays, the same approach can be used as described in the previous section. This is not recommended as a general practice; in addition to disabling the Windows 8.1 DPI feature benefits, it also results in making display content significantly smaller than optimal. As a result, we recommend that only users customize their DPI scaling on these devices.